Furnaces of various designs for heating steel parts and components employ atmospheres chiefly composed of nitrogen and carbon compounds, so that specific qualities, such as hardness and ductility, can be achieved.
Traditionally, heat-treating furnace atmospheres were obtained from endothermic generators, which employ natural gas and produce atmospheres of various humidity levels, dependent upon combustion and outdoor atmospheric conditions. Often, dryers are employed to control excess humidity.
More recently, endothermic generators have been replaced by systems utilizing gaseous flows of nitrogen and methanol from stored sources, the required flows being controlled by flow control panels.
Heat treating processes, such as annealing, require dry atmospheres (corresponding to a dew point of approximately -10.degree. to +10.degree. F.) for which nitrogen/methanol atmospheres are ideally suited. However, some processes, such as copper coating on steel, require higher humidity atmospheres (corresponding to a dew point in the range of about +40.degree. F.).
This requirement has led to a search for a system to introduce humidity while excluding oxygen, which is an undesired component in these processes. Various procedures are being utilized, for example, bubbling nitrogen through a packed wet column, so that nitrogen becomes humidified by picking up water. However, precise humidity levels are not easily maintained.
The present invention is directed towards the provision of an improved humidifying method and apparatus which enables furnace atmosphere humidity levels to be controlled and more precisely maintained. A search has been conducted in the facilities of the United States Patent and Trademark Office with respect to the invention and the following U.S. patents have been noted as the closest prior art:
______________________________________ U.S. 3,486,697 R. F. Fraser 3,721,431 Nishida 3,801,380 Ebner 3,830,478 Pietroni 4,547,228 Girrell et al 4,632,707 Shay et al ______________________________________
The cited prior art describes a variety of annealing processes as well as procedures for humidifying the atmosphere employed in such annealing processes. In general, humidification is provided by steam. One problem with steam is that small amounts of steam contain only small amounts of heat and hence, upon mixing with a nitrogen feed stream, there is a tendency for the steam to condense out of the gas stream, thereby significantly decreasing its effectiveness.